One of the first things to consider when purchasing a gas furnace is its efficiency. This is indicated by the Annual Fuel Utilization Efficiency rating or AFUE. Trane offers a variety of highly efficient gas furnaces, ranging from 78% to 93% efficiency. Trane also offers variable-speed and two-stage furnaces, which can greatly increase your comfort level. Take a look at the Trane heating family below and find the furnace that best fits your needs.